1. Field of the Invention
The present invention relates to a positive-working highly-heatproof photosensitive resin composition usable for surface protective film and interlayer insulation film of semiconductor devices, or interlayer insulation film of display devices, and to a method of producing cured relief patterns having high resistance to heat by use of such a positive-working highly-heatproof photosensitive resin composition, and further to a semiconductor device including such relief patterns.
2. Description of the Related Art
As surface protective film and interlayer insulation film for use in semiconductor devices, films formed from negative-working polyimide resins are currently in use because they have both high heat resistance and excellent electric and mechanical characteristics. At present, negative-working polyimide resins are generally made available for use in the form of photosensitive polyimide precursor compositions, and these precursor compositions can easily form surface protective films or interlayer insulation films in semiconductor devices by being subjected successively to coating, patterning with actinic rays, development with organic solvent, thermal imidization treatment at high temperatures, and so on. Therefore, they have a feature that they can significantly curtail the film formation process, compared with traditional non-photosensitive polyimide precursor compositions.
However, the photosensitive negative-working polyimide precursor compositions require large volumes of organic solvents as developer, such as N-methyl-2-pyrrolidone, in their respective development processes, so some way out of organic solvent use has been required from recently growing concerns about environmental problems. In response to this requirement, as is the case with photoresists, various heat-resistant photosensitive resin materials developable with alkaline aqueous solutions have been put forth just of late.
Of such proposals, latest attention has been given to the method of using as the positive-working photosensitive composition a polybenzoxazole (hereafter referred to as PBO also) precursor composition obtained by mixing a hydroxypolyamide soluble in alkaline aqueous solutions, such as a PBO precursor, with a photoactivatable ingredient such as a photosensitive diazoquinone compound.
The development mechanism of the positive-working photosensitive resin utilizes such a characteristic of the photosensitive diazoquinone compound that, while the photosensitive diazoquinone compound in unexposed portions is insoluble in alkaline aqueous solutions, the photosensitive diazoquinone compound causes a chemical change by undergoing exposure to be converted into an indenecarboxylic acid compound and be rendered soluble in alkaline aqueous solutions. In other words, a difference between exposed and unexposed portions with respect to the rate of dissolution in a developer is utilized and formation of relief patterns made up of unexposed portions alone becomes possible (See, e.g., JP-A-56-27140).
On the other hand, in the field of semiconductor photoresists, a multiplicity of chemical amplification photosensitive compositions producing catalytic amounts of acids upon exposure and, in a subsequent heating process, converting their alkali-insoluble groups into alkali-soluble groups through chemical reaction utilizing as catalyst the acids generated by the exposure have been used suitably as techniques to separate photosensitivity from insolubility of unexposed portions. In the present technical field also, chemical amplification photosensitive compositions are disclosed (See, e.g., JP-A-2002-526793).
However, with recent evolution of semiconductor technology, there has been more need for formation of finer patterns and decrease in curing temperature (curing temperature) after pattern formation.
When the curing temperature in particular is lowered, it is known that thermal benzoxazole-ring formation becomes difficult to advance. On this problem, a report of improvements by addition of sulfonic acid or a sulfonate compound has already been made (See JP-A-2006-010781). However, cases have been found where the film obtained was lacking in strength and chemical resistance or suffered damage to its fine-image formability.
On the other hand, there are proposals of the arts of adding various methylol compounds and thereby preventing film melt or heat-shrinkage from occurring at the time of curing by heat without impairment of lithography performance (JP-A-2001-312063, JP-A-2006-178437, JP-A-2002-169283 and JP-A2005-043883). However, in the cases of carrying out the curing under low-temperature conditions, it has been found that the film cured was great in thermal weight reduction and inferior in heat resistance.
In other words, materials capable of delivering excellent performance (film remaining rate and resolution) in lithography, being cured at low temperatures of 300° C. or below, preferably 250° C. or below, and showing satisfactorily high heat resistance have not been discovered yet.